UBIFS: fix memory leak on error path

UBIFS: fix memory leak on error path

commit 812eb258311f89bcd664a34a620f249d54a2cd83 upstream.

UBIFS leaks memory on error path in 'ubifs_jnl_update()' in case of write
failure because it forgets to free the 'struct ubifs_dent_node *dent' object.
Although the object is small, the alignment can make it large - e.g., 2KiB
if the min. I/O unit is 2KiB.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>